Narrative:Two Air Cargo Carriers Shorts 360 cargo planes, N372AC and N3735W, had been in maintenance for the installation of some auxiliary fuel tanks. Flights were planned to verify the fuel flow rates for those tanks. Prior to departure, both flight crews decided that they would join-up after departure in order to take video and still photography of each airplane. N3735W and N372AC departed Milwaukee (MKE) at 15:55 and 16:15, respectively. After departure and clearing MKE airspace, the flight crew of N372AC established radio and visual contact with N3735W. N3735W then proceeded to perform several fly-bys past N372AC who remained on constant headings and altitude. N3735W then came up along the other Shorts' left side and flew in formation with approximately 100-150 feet lateral separation. A pilot of N3735W then announced over the radio that they would turn right and descend below N372AC. During that manoeuver N3735W's left wing impacted the left wing and engine of the other plane. The captain of N372AC attempted to climb in an attempt to avoid impacting N3735W. The outboard 3/4 of the left wing of N3735W separated and the airplane crashed out of control, into a field southeast of the intersection of Highway Q and Highway 19 and caught fire. After the collision, N372AC rolled to the left and pitched down significantly before the flight crew regained control of the airplane. The flight crew declared an emergency and diverted to Juneau-Dodge County Airport, WI (UNU) for an emergency landing. N372AC experienced a complete hydraulic failure and was losing hydraulic fluid. The flight crew performed an emergency landing on runway 08 (5,069 feet by 100 feet, asphalt) with flaps retracted and a partially extended landing gear. The airplane overran the end of the runway, coming to rest about 100 feet from the departure threshold.
PROBABLE CAUSE: "The flight crew failed to maintain clearance from another aircraft as they turned to break formation flight while maneuvering. Contributing to the accident was the decision of both flight crews to fly in formation."
Mid air collision
Forced landing on runway
VH-SUM was sold as N372AC in November 2003, ending up at Air Cargo Carriers in 2005